Mycotoxins: Biosecurity, Food Safety and Biofuels Byproducts (NC129, NC1025)

Non-Technical Summary:<br/>
Aflatoxins are cancer-causing toxins produced by a naturally and ubiquitously occurring moldy fungus Aspergillus flavus. Crops contaminated with aflatoxins are unsafe for food and industry purposes. In the southeastern region of the United States, the infection of Aspergillus flavus in maize is a chronic problem. Commercial maize hybrids are generally susceptible to Aspergillus flavus. Significant levels of corn host plant resistance to the fungus have been bred into some inbred maize lines such as Mp313E and Mp715. However, the resistance must be integrated into commercial maize lines to improve corn production. The corn host resistance to Aspergillus flavus infection and aflatoxin accumulation is a trait controlled by many genes. Progresses have been made to increase corn host plant resistance by conventional crop breeding. It has become apparent that it is hard to transfer all the resistance from one maize inbred line to another without first identifying the resistance genes and their effects. Identification of as many corn resistance genes as possible will speed up molecular marker aided resistance breeding. The proposed research projects here are set to identify corn host resistance genes associated with Aspergilus flavus infection using functional genomics tools. In addition, investigations on the fungal gene markers associated with aflatoxin-producing and non-aflatoxin producing Aspergilli ssp. will be conducted to facilitate the principal research objectives.
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Approach:<br/>
The objectives of this research project are to isolate and identify resistance-related maize proteins/genes associated with Aspergillus flavus infection and aflatoxin contamination. Maize germplasm exhibiting resistance or susceptibility to Aspergillus flavus infection and aflatoxin accumulation are used for genome wide comparative analysis on gene/RNA/Protein expression levels. Samples are collected from field maize plants with appropriate experimental design for statistical analysis. Kernels from ears with or without inoculation of Aspergillus flavus are collected at different time points. Maize protein/DNA/RNA are then extracted from resistant and susceptible maize samples. Genomics/proteomics/transcriptomics/bioinformatics tools are incorporated to facilitate the identification of genetic factors involved in maize resistance to Aspergillus flavus infection and aflatoxin accumulation. Candidate gene sequences will be provided for use as potential molecular markers to assist resistant maize breeding.
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Progress:<br/>
2012/01 TO 2012/12<br/>
OUTPUTS: Annual Report Project Title: Identification of genes associated with resistance to Aspergillus flavus infection and aflatoxin accumulation in maize. The research goals and objectives were centered on the identification of genes associated with resistance to Aspergillus flavus infection and aflatoxin accumulation in maize. Special goals for this period were set to compare gene expression levels in resistant and susceptible maize inbred lines (Mp313E, B73,Va35, and Mp04:86). An efficient protocol was established to solve the major computational obstacles in analysis of high throughput gene expression data for the identification of differentially expressed genes. This protocol was effective in both microarray experiments and qRT-PCR experiments.
<br/>PARTICIPANTS: Participants: Xueyan Shan, Renuka Shivaji, J. Erik Mylroie, Alka Tiwari, Kristin Matzek, Matthew Asters, S. Kate Thompson (Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University). Collaborators: W. Paul Williams, Gary L. Windham, Marilyn Warburton, Leigh Hawkins (Partner Organizations: USDA-ARS, Corn Host Plant Resistance Research Unit, Mississippi State, Mississippi).
<br/>TARGET AUDIENCES: Scientists, graduate students, and undergraduate students.
<br/>PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
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IMPACT: Accomplishments achieved: 1) Sixteen candidate genes were found to be highly expressed in the resistant corn inbred line Mp313E and fifteen in the susceptible Va35. Out of the 31 highly expressed genes, eight were mapped to seven previously identified quantitative trait locus (QTL) regions. For example, a gene encoding glycine-rich RNA binding protein 2 (AI664980) was found to be associated with the host hypersensitivity and susceptibility in Va35. A nuclear pore complex protein NUP85-like gene (TC231674) was found to be involved in the host resistance in Mp313E. 2)The followings are some details on the findings: TC231674 is the highest expressed found in Mp313E samples. TC231674 encodes a NUP85-like gene that is a part of a sub-complex of the nuclear pore complexes (NPCs) embedded in the nuclear envelope. The function of NPCs is for the transport of RNA and other macromolecules from nucleus to cytoplasm. TC237311 and BM379345 are second highest in expression. TC237311 encodes the heat shock protein HSP101. This protein acts as a molecular chaperone to disaggregate mis-folded proteins. BM379345 encodes a metallothionein like protein (MTLP) that is involved in the binding and detoxification of heavy metal ions. BE050050 and TC238832 comprise the next level in expression. BE050050 has no annotation available. TC238832 encodes a lecithin cholesterol acyltransferase (LCAT)-like gene. Other highly expressed genes include BM498943, BM078796, and TC207503. BM498943 encodes ethylene responsive protein (ETHRP) that belongs to the universal stress protein family. BM078796 encodes small heat shock protein HSP26. TC207503 encodes a prenylated rab acceptor (PRA1) family protein. Prenylated Rab PRA1 proteins are small transmembrane proteins that regulate vesicle trafficking. 3)These findings will be important in identification of DNA markers for breeding maize lines resistant to aflatoxin accumulation. Genes significantly associated with resistance are being further evaluated by scientsts in the USDA-ARS Corn Host Plant Resistance Research Unit in Mississippi State. Polymorphisms in TC238832 and TC231674 sequences were found to differentiate resistant and susceptible corn inbred lines in a preliminary test.